The present invention relates to a process for the preparation of a suspension which contains sphere-shaped oxide particles, and in particular to a process in which the sphere-shaped oxide particles are prepared in a water-in-oil emulsion with the aid of a compound which acts as a phase transfer catalyst. The invention furthermore relates to the use of the suspensions obtained in such a process for the preparation of (ceramic) oxide powders and/or (ceramic) shaped articles.
A plurality of processes for the preparation of powders from emulsions is described in the literature. An example of this is the emulsification of metal alkoxides in liquids which are immiscible therewith (for example paraffin oil or propylene carbonate), followed by hydrolysis. The main disadvantage of this process is that the required alkoxides are relatively expensive compounds. In another existing process, salt solutions or stabilized sols are emulsified in hydrocarbons, and then, for example, ammonia is passed in to precipitate hydroxides, and the resulting mixture is added dropwise to boiling hydrocarbons so that the water evaporates, or the mixture is freeze-dried. The dry powders which can be obtained by this process contain the anions in the form of metal salts or ammonium salts. Thermal decomposition, which then takes place, brings about disintegration of the particles or the formation of open-pore, sponge-like structures. High green densities and good sinter properties can only be achieved by these processes in individual cases, if at all.
In yet another existing process the extraction of acids or anions of acid salts from emulsified aqueous phases is achieved by adding long-chain amines to the organic phase. However, a complete exchange requires a large excess of amines or step-wise extraction. Such a process is not capable of splitting neutral salts (for example alkali metal compounds or alkaline earth metal compounds).